Wobble detecting apparatus

ABSTRACT

A wobble detecting apparatus for an information recording and/or reproducing for an optical disk, includes a wobble detecting unit for detecting a wobble on the basis of a signal from a light receiving element which receives light reflected from the optical disk; an offset voltage generating unit for generating an offset voltage; an adder unit for adding said offset voltage to a control signal to an actuator for the optical disk; an actuator switch for on/off controlling a control signal to said actuator; and a control unit for turning on said actuator for wobble detection to decide whether or not the wobble has been detected by said wobble detecting unit, and if the wobble has not been detected, causing said offset voltage generating unit to generate a positive or negative prescribed voltage to decide further whether or not the wobble has been detected by said wobble detecting unit. In this configuration, the wobble can be detected with high accuracy.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a wobble detecting apparatus fordetecting a wobble signal of an optical disk in a device for recordingand/or reproducing information for the optical disk.

[0003] 2. Description of the Related Art

[0004] In an optical disk such as a writable CD or DVD, as shown in FIG.10, a track 1A of an optical disk 1 on which information is to be storedwobbles. The wobble is detected to reproduce a clock signal at the timeof the write.

[0005] In the device for recording and/or reproducing information forthe optical disk, as the case may be, the presence or absence of thewobble is decided to determine whether the optical disk loaded in thedevice is recordable or dedicated to only reproduction.

[0006] In the device for recording and/or reproducing information for anoptical disk, laser light is focused, the focused light is projected onthe optical disk, and the light reflected from the optical disk isreceived by a light receiving element, thereby providing a wobblesignal, a tracking signal, a focus signal and a reproduction signal.

[0007]FIG. 11 shows relative positions of a light receiving element anda received light spot 21 of the reflected light projected on the lightreceiving element 4.

[0008] The light receiving element 4 is partitioned into four sectionsA, B, C and D. In shipping the device, as seen from FIG. 11B, adjustmentis made so that the received light spot is projected on the center ofthe four divided sections. This adjustment cannot be made completely. Asseen from FIG. 11A, the optical axis is misaligned leftward, orotherwise, as seen from FIG. 11C, the optical axis is misalignedrightward.

[0009] The wobble signal is obtained from a difference signal(A+B)−(C+D) on the basis of the output signals from the sections A, B, Cand D of the light receiving element 4.

[0010] As seen from FIGS. 11A and 11C, when the received light spotdeviates from the boundary between the sections A, B and C, D owing tothe misalignment of the optical axis, the S/N ratio of the wobble signalbased on the difference signal (A+B)−(C+D) is deteriorated, and hencethe presence or absence of the wobble signal cannot be detectedprecisely.

SUMMARY OF THE INVENTION

[0011] An object of this invention is to provide a wobble signaldetecting apparatus which can detect the presence or absence of awobble.

[0012] In order to attain the above object, in accordance with an aspectof this invention, there is provided a wobble detecting apparatus for adevice for recording and/or reproducing information for an optical disk,comprising:

[0013] a wobble detecting unit for detecting a wobble on the basis of asignal from a light receiving element which receives light reflectedfrom the optical disk;

[0014] an offset voltage generating unit for generating an offsetvoltage;

[0015] an adder unit for adding the offset voltage to a control signalto an actuator for the optical disk;

[0016] an actuator switch for on/off controlling a control signal to theactuator; and

[0017] a control unit for turning on the actuator for wobble detectionto decide whether or not the wobble has been detected by the wobbledetecting unit, and if the wobble has not been detected, causing theoffset voltage generating unit to generate a positive or negativeprescribed voltage to decide further whether or not the wobble has beendetected by the wobble detecting unit.

[0018] In a preferred embodiment, where the wobble has not been detectedby the wobble detecting unit when the positive or negative prescribedvoltage is generated by the offset voltage generating unit, the controlunit causes the offset voltage generating unit to generate a new offsetvoltage of the prescribed voltage plus the offset voltage previouslyproduced, thereby causing the wobble detecting unit to repeat the wobbledetection by a prescribed number of times.

[0019] In accordance with another aspect of this invention, there isprovided a wobble detecting apparatus for a device for recording and/orreproducing information for an optical disk, comprising:

[0020] a wobble detecting unit for detecting a wobble on the basis of asignal from a light receiving element which receives light reflectedfrom the optical disk;

[0021] an offset voltage generating unit for generating an offsetvoltage;

[0022] an adder unit for adding the offset voltage to a control signalto an actuator for the optical disk;

[0023] an actuator switch for on/off controlling a control signal to theactuator;

[0024] an carriage switch for on/off controlling a control signal to acarriage on which the actuator is loaded; and

[0025] a control unit for turning on the carriage switch turning on theactuator for wobble detection and causing the offset voltage generatingunit to generate a prescribed voltage to decide whether or not thewobble has been detected by the wobble detecting unit.

[0026] In a preferred embodiment of another aspect of this invention,the control unit counts the number of rotation of the optical disk fromwhen wobble detection is started, and confirms non-detection of thewobble if the wobble has not detected when the counted value reaches aprescribed number of times.

[0027] In accordance with still another aspect of this invention, thereis provided a wobble detecting apparatus for a device for recordingand/or reproducing information for an optical disk, comprising:

[0028] a wobble detecting unit for detecting a wobble on the basis of asignal from a light receiving element which receives light reflectedfrom the optical disk;

[0029] a low pass filter for passing a DC component of a differencesignal produced from the light emitting element;

[0030] an offset voltage generating unit for generating an offsetvoltage;

[0031] an adder unit for adding the offset voltage to a control signalto an actuator for the optical disk;

[0032] an actuator switch for on/off controlling a control signal to theactuator; and

[0033] a control unit for turning off the actuator for wobble detection,causing the offset voltage generating unit to generate the offsetvoltage so that an output form the low pass filter is zero, turning onthe actuator switch when the output from the low pass filter has becomeapproximately zero, and deciding whether or not the wobble has beendetected by the wobble detecting unit.

[0034] In accordance with this invention, an actuator is moved torealize the state with no misalignment of an optical axis, and in thisstate, a wobble is detected. Therefore, S/N can be improved and thepresence or absence of the wobble can be detected accurately.

[0035] The above and other objects and features of the invention will bemore apparent from the following description taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is an arrangement view of a first embodiment of thisinvention;

[0037]FIG. 2 is a block diagram showing an example of a wobble detectingunit;

[0038]FIGS. 3 and 4 are flowcharts for explaining the operation of thefirst embodiment of this invention;

[0039]FIG. 5 is an arrangement view of the second embodiment of thisinvention;

[0040]FIG. 6 is a flowchart of the operation of the second embodiment ofthis invention; and

[0041]FIG. 7 is an arrangement view of the third embodiment of thisinvention;

[0042]FIG. 8 is a flowchart of the operation of the third embodiment ofthis invention; and

[0043]FIG. 9A-9F are views for explaining the operation of the thirdembodiment;

[0044]FIG. 10 is a view for explaining the wobble on an optical disk;and

[0045]FIG. 11A-11C are views for explaining the misalignment of anoptical axis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] Referring to the drawings, an explanation will be given ofvarious embodiments of this invention.

[0047] Embodiment 1

[0048]FIG. 1 is an arrangement view of a first embodiment of thisinvention; FIG. 2 is a block diagram showing an example of a wobbledetecting unit; and FIGS. 3 and 4 are flowcharts for explaining theoperation of the first embodiment of this invention.

[0049] Referring to FIG. 1, reference numeral 1 denotes an optical disk;2 a carriage; 2A an actuator on which an objective lens for focusinglaser light on the optical disk 1 is loaded; 3 a driver for driving theactuator; 4 a light receiving element; 5 amatrix circuit; 6 a focuscontrol unit; 7 a tracking control unit; 8 an actuator switch; and 9 anadder unit.

[0050] In the apparatus for recording and reproducing information on andfrom the optical disk 1, the matrix circuit 5 produces an RF signal ofA+B+C+D based on the output signals from the four divided sections A, B,C and D of the light receiving element 4, and also creates e.g. (phasedifference between the RF signal and the output signal A)+(phasedifference between the RF signal and the output signal D)−(phasedifference between the RF signal and the output signal B)−(phasedifference between the RF signal and the output signal C) which is to besupplied to the tracking control unit 7. Namely, tracking is executed bythe DPD (Differential Phase Detection) technique. The recording and/orreproducing apparatus creates the signal (A+D−B−C) to be supplied to thefocus control unit 6, thereby executing the focus control.

[0051] The actuator 2A is moved according to a control voltage appliedto the driver 3. For example, if the control voltage is positive, theactuator 2A moves by a prescribed distance toward the inner periphery ofthe optical disk 1, whereas if the control voltage is negative, theactuator 2A moves by the prescribed distance toward the outer peripheryof the optical disk 1.

[0052] The actuator 2A is loaded on the carriage 2 by e.g. spring.During the tracking, the actuator 2A follows a track to move. When theactuator 2A moves by a prescribed distance, the carriage 2 moves towardthe outer periphery and then the actuator 2A is located on the center ofthe carriage 2.

[0053] The above operation is the same as that of the conventionaldevice for recording and reproducing information on and from the opticaldisk.

[0054] Incidentally, in FIG. 1, reference numeral 10 denotes a wobbledetecting unit; 11 an offset voltage generating unit; 12 a control unit;13-15 an interface (I/O); and 16 a processor (CPU).

[0055] As seen from FIG. 2, in the wobble detecting unit 10, adifference signal (A+B)−(C+D) from the light receiving element 4 isconverted into a square wave by a binary-digitizing circuit 10B througha band-pass filter (BPF) 10A passing a wobble signal frequency.

[0056] A wobble deciding circuit 10C decides that if a subsequent pulseis successively produced within a prescribed time after a certain pulseis produced from the binary-digitizing circuit 10B, there is a wobble,and if the subsequent pulse is not successively produced, there is nowobble.

[0057] Now referring to FIG. 3, an explanation will be given of theprocessing operation of the first embodiment.

[0058] When the wobble detecting operation is started, step S1 is firstexecuted.

[0059] In step S1, the control unit 12 turns on the actuator switch 8 tostart the tracking operation.

[0060] In step S2, the control unit 12 determines whether or not awobble has been detected by the wobble detecting unit 10. If YES, theprocessing proceeds to step S3. In step S3, the control unit 12 producesan output indicative of that the wobble has been detected. Theprocessing is ended.

[0061] If NO in step S2, the processing proceeds to step S4. In step S4,the control unit 12 instructs the offset voltage generating unit 11 togenerate a positive prescribed offset voltage (+V).

[0062] The prescribed offset voltage (V) is set at a voltage whichcauses the actuator 2A to move by e.g. about 10 μm.

[0063] The positive offset voltage thus generated is supplied to theadder unit 9 through the I/O 14. It is added to the tracking controlvoltage produced from the tracking control unit 7. The resultant voltageis entered into the driver 3.

[0064] When the positive offset voltage (+V) is entered into the driver3, the driver 3 causes the actuator 2A to move toward e.g. the innerperiphery of the optical disk 1.

[0065] Owing to the movement of the actuator 2A, misalignment of theoptical axis will occur.

[0066] Now assuming that the state where the offset voltage is notsuperimposed on the tracking control voltage is that shown in FIG. 11A,when the actuator 2A is moved toward the inner periphery of the opticaldisk, the state approaches the state shown in FIG. 11B where the wobbleis detected.

[0067] Assuming that the state where the offset voltage is notsuperimposed on the tracking control voltage is that shown in FIG. 11C,superimposing of the offset voltage further increases the misalignmentof the optical axis so that the light received spot 21 moves furtherrightwards, which results in the state where no wobble is detected.

[0068] In step S5, the control unit 12 determines whether or not thewobble has been detected by the wobble detecting unit 10. If YES, theprocessing proceeds to step S3. In step S3, the control unit 12 confirmsthat the wobble has been detected. The processing is ended.

[0069] If NO in step S5, the processing proceeds to step S6. In step S6,the control unit 12 determines whether or not the prescribed voltage hasbeen generated by a prescribed number of times. If NO in step S6, theprocessing proceeds to step S7.

[0070] In step S7, the control unit 12 instructs the offset voltagegenerating unit 11 to generate a voltage resulting from addition of theprescribed voltage (+V) to the offset voltage (+V) which is beinggenerated, thus generating an offset voltage of +nV (n: number ofgeneration times). In this way, steps S4-step S7 are repeated.

[0071] Incidentally, assuming that the maximum value of the misalignmentof the optical axis in shipping the information recording and/orreproducing device is ±80 μm, the prescribed number of times N is set at8. If the wobble is not detected even when the offset voltage +V isgenerated to move the actuator 2A by +10 μm, +2V (n=2) is generated tomove the actuator 2A by +20 μm to detect whether or not the wobble hasbeen detected.

[0072] Even with n=8, if no wobble is detected, under the decision thestate will not approach the state shown in FIG. 11B even if thealignment of the optical disk is generated in the +direction, theprocessing proceeds to step S8. Steps S8 to S11 are executed.

[0073] In step S8, the control unit 12 instructs the offset voltagegenerating unit 11 to generate a negative prescribed offset voltage (−V). The same processing S8-S11 as steps S4 to S7 is repeated.

[0074] If it is determined in step S10 that the prescribed negativevoltage has been generated by the prescribed number of times, theprocessing proceeds to step S12. In step S12, the control unit 12produces an output indicative of that no wobble has been detected. Theprocessing is ended.

[0075] Embodiment 2

[0076] Referring to FIGS. 5 and 6, an explanation will be given of thesecond embodiment of this invention. FIG. 5 is an arrangement view ofthe second embodiment of this invention, and FIG. 6 is a flowchart ofthe operation of the second embodiment of this invention.

[0077] In the arrangement according to the second embodiment, as seenfrom FIG. 5, a carriage control unit 7A, a carriage switch 8A and an I/O17 are added to the arrangement of the first embodiment explainedreferring to FIG. 1.

[0078] Referring to FIG. 6, an explanation will be given of theoperation of the second embodiment.

[0079] In step S21, the control unit 12 turns OFF the actuator switch 8and in step S22, the control unit 12 turns OFF the carriage switch 8A.

[0080] In step S23, the control unit 12 instructs the offset voltagegenerating unit 111 to generate an offset voltage (+Vo) The positiveoffset voltage thus generated is supplied to the adder unit 9 throughthe I/O 14.

[0081] When the offset voltage (+Vo) is entered into the adder unit 9,the actuator 2A moves by e.g. 80 μm toward the inner periphery of theoptical disk 1.

[0082] In step S24, the control unit 12 turns ON the actuator switch 8.When the actuator switch 8 is turned ON and the carriage switch 8A isturned OFF, the actuator 2A moves from the inner periphery to the outerperiphery as the optical disk 1 rotates, thus generating themisalignment of the optical axis.

[0083] In step S25, the control unit 12 determines whether or not awobble has been detected by the wobble detecting unit 10. If YES, theprocessing proceeds to step S26. The control unit 12 produces an outputindicative of that the wobble has been detected. The processing isended.

[0084] If NO in step S25, i.e. no wobble has been detected, theprocessing proceeds to step S27. In step S27, the control unit 12 countsthe number of times of rotation of the optical disk 1 on the basis ofthe rotation information of the optical disk 1 supplied through the I/O17 to determine whether or not the counted value has reached aprescribed number of times. If NO, the processing reverts to step S25.The processing of steps S25 to S27 is repeated.

[0085] If YES, i.e. the counted value has reached the prescribed numberof times, the processing proceed to step S28. The processing is ended.

[0086] As described above, the actuator 2A is moved toward the innerperiphery of the optical disk by superposition of the offset voltage(+V). This is because it is not clear in which state of FIG. 11A andFIG. 11C, the misalignment of the optical axis is when detection of thewobble is started.

[0087] When the actuator switch 8 is turned ON and the carriage switch8A is turned OFF, as described above, as the optical disk 1 rotates, theactuator 2A moves from the inner periphery of the optical disk to theouter periphery thereof.

[0088] If the misalignment of the optical axis is in the state of FIG.11C, the misalignment is corrected as the actuator 2A moves toward theouter periphery so that the present state approaches the state of FIG.11B.

[0089] However, if the misalignment of the optical axis is in thepresent state of FIG. 11A, the misalignment is further increased as theactuator 2A moves toward the output periphery.

[0090] In this case, in step S23, the offset voltage (+V) is generatedto move the actuator 2A toward the inner periphery by e.g. 80 μm so thatthe optical axis is in the state of FIG. 11C. Further, the actuator 2Ais moved as the optical disk 1 rotates. Thus, the state of the opticalaxis approaches the state with no misalignment as shown in FIG. 11B.

[0091] Assuming that when the optical disk 1 rotates once, a spiraltrack thereon moves by 1 μm, in order that the actuator 2A moves by 80μm×2, the optical disk 1 must be rotated by 160 turns. Therefore, theprescribed number of times of rotation in step S27 is set at 160.

[0092] Embodiment 3

[0093] Referring to FIGS. 7 and 8, an explanation will be given of thethird embodiment of this invention.

[0094]FIG. 7 is an arrangement view of the third embodiment of thisinvention; and FIG. 8 is a flowchart of the operation of the thirdembodiment of this invention.

[0095] In the arrangement of the third embodiment of this invention, asseen from FIG. 7, a low pass filter (LPF) 18 for passing a DC componentand I/O 19 are added to the arrangement of the first embodiment of thisinvention as shown in FIG. 1.

[0096] Referring to FIG. 8, an explanation will be given of theoperation of the third embodiment.

[0097] In step S31, the control unit 12 turns OFF the actuator switch 8through the I/O 13.

[0098] In step S32, the control unit 12 reads the output value from theLPF 18 through the I/O 19.

[0099] In step S33, the control unit 12 determines whether or not theoutput value from the LPF 18 is 0±α (α is an error providing anegligible influence on the wobble detection). If YES, the processingproceeds to step S37.

[0100] In step S34, the control unit 12 determines whether or not theoutput from the LPF 18 is negative or positive. If positive, in stepS35, the control unit 12 instructs the offset voltage generating unit 11to generate an offset voltage which increases by an amount correspondingto the absolute value of the output value of the LPF 18 in a directionfrom 0 to negative and add the generated offset voltage to the adderunit 9 through the I/O 14. Further, the processing reverts to step S32.The processing from step S32 to S25 is repeated until the decision ofstep S33 becomes YES.

[0101] If negative in step S34, the processing proceeds to step S36. Instep S35, the control unit 12 instructs the offset voltage generatingunit 11 to generate an offset voltage which increases by an amountcorresponding to the absolute value of the output value of the LPF 18 ina direction from 0 to positve and add the generated offset voltage tothe adder unit 9 through the I/O 14. Further, the processing reverts tostep S32. The processing from step S32 to S35 and S36 is repeated untilthe decision of step S33 becomes YES.

[0102] In step S33, if YES, i.e., the output from the LPF 18 becomes0±α, the processing proceeds to step S37. In step S37, the control unit12 turns ON the actuator switch 8. In step S38, the control unit 12determines whether or not a wobble has been detected by the wobbledetecting unit 10. If YES, the control unit 12 produces an outputindicative of that the wobble has been detected. If NO, the control unit12 produces an output indicative of that no wobble has been detected.Thus, the processing is ended.

[0103] As described above, in steps S35 and S36, the offset voltagecorresponding to the absolute value of the LPF output value isgenerated. In this case, the relationship between the LPF output valueand the offset value to be added for its correction differs according tothe characteristic of an optical system of a product. Therefore, theconversion coefficient from the LPF output value in each product intothe offset voltage may be previously set.

[0104] In step S33, if the output from the LPF 18 is within apermissible range of 0±α, the processing proceeds to step S37. In stepS37, the control unit 12 turns OFF the actuator 8 to detect the wobble.This reason will be explained referring to FIG. 9.

[0105]FIGS. 9A, 9B and 9C show relative positions of the light receivingelement 4 and the light received spot. FIGS. 9D, 9E and 9F shows awaveform of a difference signal A+B−C−D produced from the matrix circuit5 when the optical disk 1 is rotated once with the actuator switch 8being in the OFF state.

[0106] In the case where there is no misalignment of the optical axis asshown in FIG. 9B, the matrix circuit 5 produces the difference signalA+B−C−D as shown in FIG. 9E, i.e. a sinusoidal difference signalwhenever the spot of the laser light projected on the optical disk 1crosses a track. The DC component thereof is zero.

[0107] However, if there is a misalignment of the optical axis as shownin FIGS. 9A and 9B, a positive or negative DC component is superimposedon the sinusoidal difference signal.

[0108] Therefore, in the processing of steps S32-S38, the offset voltageis generated from the offset voltage generating unit 11 to move theactuator 2A so that the state of FIG. 9A or 9C is shifted into the stateof FIG. 9B with no misalignment of the optical axis, in step S37, theactuator switch 8 is turned ON, and in step S38, the wobble is detected.

[0109] In the third embodiment, the polarity and amount of the generatedoffset voltage can be known from the polarity and absolute value of theoutput of the LPF 18. Therefore, the offset voltage is generated, andwhen the output for the LPF 18 is 0±α, the actuator switch 8 is turnedON to detect the wobble. In this way, the wobble can be detected in ashort time.

[0110] Incidentally, the contents of Japanese Patent Appln. No.2000-252324 (filed Aug. 28, 2000) are hereby incorporated by reference.

What is claimed is:
 1. A wobble detecting apparatus for a device forrecording and/or reproducing information for an optical disk,comprising: a wobble detecting unit for detecting a wobble on the basisof a signal from a light receiving element which receives lightreflected from the optical disk; an offset voltage generating unit forgenerating an offset voltage; an adder unit for adding said offsetvoltage to a control signal to an actuator for the optical disk; anactuator switch for on/off controlling a control signal to saidactuator; and a control unit for turning on said actuator for wobbledetection to decide whether or not the wobble has been detected by saidwobble detecting unit, and if the wobble has not been detected, causingsaid offset voltage generating unit to generate a positive or negativeprescribed voltage to decide further whether or not the wobble has beendetected by said wobble detecting unit.
 2. A wobble detecting apparatusaccording to claim 1, wherein where the wobble has not been detected bythe wobble detecting unit when said positive or negative prescribedvoltage is generated by said offset voltage generating unit, saidcontrol unit causes said offset voltage generating unit to generate anew offset voltage of said prescribed voltage plus the offset voltagepreviously produced, thereby causing the wobble detecting unit to repeatthe wobble detection by a prescribed number of times.
 3. A wobbledetecting apparatus for a device for recording and/or reproducinginformation for an optical disk, comprising: a wobble detecting unit fordetecting a wobble on the basis of a signal from a light receivingelement which receives light reflected from the optical disk; an offsetvoltage generating unit for generating an offset voltage; an adder unitfor adding said offset voltage to a control signal to an actuator forthe optical disk; an actuator switch for on/off controlling a controlsignal to said actuator; an carriage switch for on/off controlling acontrol signal to a carriage on which said actuator is loaded; and acontrol unit for turning on said carriage switch turning on saidactuator for wobble detection and causing said offset voltage generatingunit to generate a prescribed voltage to decide whether or not thewobble has been detected by said wobble detecting unit.
 4. A wobbledetecting apparatus according to claim 3, wherein said control unitcounts the number of rotation of the optical disk from when wobbledetection is started, and confirms non-detection of the wobble if thewobble has not detected when the counted value reaches a prescribednumber of times.
 5. A wobble detecting apparatus for a device forrecording and/or reproducing information for an optical disk,comprising: a wobble detecting unit for detecting a wobble on the basisof a signal from a light receiving element which receives lightreflected from the optical disk; a low pass filter for passing a DCcomponent of a difference signal produced from said light emittingelement; an offset voltage generating unit for generating an offsetvoltage; an adder unit for adding said offset voltage to a controlsignal to an actuator for the optical disk; an actuator switch foron/off controlling a control signal to said actuator; and a control unitfor turning off said actuator for wobble detection, causing said offsetvoltage generating unit to generate the offset voltage so that an outputform said low pass filter is zero, turning on said actuator switch whenthe output from said low pass filter has become approximately zero, anddeciding whether or not the wobble has been detected by said wobbledetecting unit.